The present invention relates to oil-filled transformer housings composed of a tank in which a transformer is to installed so as to be immersed in oil and a base for supporting the tank, and particularly to devices for use in attaching the tank to the base.
Oil-filled transformer housings typically include components of the type described above. The tank and base must be manufactured individually, with a protective coating, for example an electrostatic paint coating, applied at least to the tank before the tank and base are assembled together. The tank and base may be secured together by welding or by attachment devices, each device including a component which is permanently secured to the tank bottom.
While it is known to secure the tank and base together by welding, this approach offers a number of disadvantages, including the fact that it prevents the two parts from being painted separately, and thus results in less complete paint coverage, and requires that the tank and base be assembled together during the manufacturing procedure rather than at a later time.
For these reasons, various types of mechanical fastening arrangements have been proposed. One of these arrangements includes carriage bolts inserted horizontally through openings in a lip extending beyond the bottom of the tank and through mating openings provided in the side walls of the base. One disadvantage of this approach is that it requires perfect alignment of the holes in the tank and the base.
Other proposed techniques involve various types of clamping devices all of which require the permanent fastening of projecting parts to the bottom of the tank during tank fabrication, and in particular prior to application of a protective coating to the tank. These devices all present a number of drawbacks.
Thus, since the parts which are permanently attached to the tank project downwardly from the bottom, they create difficulties when the tank is to be carried by a conveyer. In addition, they cause distortion of the bottom of the tank during leak testing and require a substantial amount of welding. It is difficult to effect accurate positioning of the parts to be welded and to subsequently achieve adequate protective coating coverage around and under the welded parts to assure satisfactory corrosion resistance. Moreover, the known parts permanently fastened to the tank bottom are of such a nature that additional means are required for suspending the tanks from their bottoms in order to carry out the coating operation.
Furthermore, standards governing transformer installations, such as those issued by ANSI and NEMA, specify that such installations shall be constructed to prevent insertion of a wire having a specified size between the tank and the base. Various structures of a more or less complicated nature have been proposed for the purpose of satisfying this standard.